Gas turbines are widely used in industrial and commercial operations. A typical gas turbine includes a compressor section at the front, one or more combustors around the middle, and a turbine section at the rear. The compressor section includes multiple stages of rotating blades and stationary vanes. Ambient air enters the compressor section, and the rotating blades and stationary vanes progressively impart kinetic energy to the working fluid (air) to bring it to a highly energized state. The working fluid exits the compressor section and flows to the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases exit the combustors and flow to the turbine section where they expand to produce work.
An exhaust diffuser downstream of the turbine section converts the kinetic energy of the flow exiting the last stage of the turbine section into potential energy in the form of increased static pressure. This is accomplished by conducting the flow through a duct of increasing area, during which the generation of total pressure loss is to be minimized. The exhaust diffuser typically includes one or more aerodynamic airfoils which surround structural struts that may support a rotor bearing.
Exhaust gases from the turbine section enter the exhaust diffuser with a wide range of inlet swirl conditions across the load range of the gas turbine section. The varying swirl conditions may cause the exhaust gases to intercept and flow over the struts at varying incidence angles, resulting in significant aerodynamic losses such as pressure loss due to flow separation as the exhaust gases flow across the struts. In addition, high swirl at the inlet of the diffuser has the potential for causing mechanical excitation within the diffuser due to vortex shedding from the strut. Therefore, it is desirable to be able to reduce the flow separation across the diffuser struts to enhance the aerodynamic performance of the gas turbine.